Sealing compound comprising cork powder and talc fillers

ABSTRACT

A PVC-free sealing compound, particularly a sealing compound for use on containers, comprising a mixture of low density polyethylene or linear low density polyethylene; a styrene-isoprene-styrene block copolymer or a thermoplastic elastomeric blend of an ethylene-propylene copolymer such as EPM or EPDM, EVA and process oil, one or more fillers such as talc, and optionally cork powder.

The present invention relates to sealing compounds, particularly sealingcompounds suitable for use on container closures.

BACKGROUND

Seals for use on container closures, such as metal crowns, rolled oncaps or plastic caps are conventionally made from sealing compoundsbased on a PVC-plastisol system. Such compounds are usually lined intothe closure as a liquid and fluxed to form the seal. Some seals havebeen formed using a PVC-based compound in which the compound is formedinto an extruded form such as pellets which are deposited into theclosure and shaped into the appropriate seal by means of a die.

Seals for container closures, such as bottle caps, must have specificcharacteristics in order to adequately seal a container. The seal mustbe soft enough so as to adapt to any possible irregularities of thecontainer edge, such as a bottle neck, especially on a reused glassbottle. Simultaneously, the seal must be adequately elastic to maintainthe seal between the closure and the container, especially when thecontainer holds a pressurized product, such as beer or tonic. The sealsmust also serve as barriers to the ingress or egress of water vapor andoxygen. This is especially important in connection with the keepingqualities of beer, which is adversely affected by oxygen. Finally, theseal itself must not alter the taste of the packed product.

PVC-based compounds adequately fulfill these characteristics, though theuse of PVC has been objected to because of its waste disposal problemsand in particular, because of the health risks which have been claimedfrom the use of PVC on food packs. There has therefore been an increaseddemand for compounds which are free of PVC, yet have the same sealingcharacteristics as PVC.

Some attempts have been made to make sealing compounds based onpolyethylene, though they have not gained any widespread acceptance dueto their inferior characteristics as compared to PVC-based compounds.Some characteristics have been enhanced through the addition of variousadditives, but the additives make the compounds so expensive that theyre not competitive or marketable.

SUMMARY OF THE INVENTION

The present invention is a relatively inexpensive sealing compound whichis PVC-free and has excellent sealing characteristics. The presentinvention is a polyethlene-based compound containing selected elastomersand suitable fillers.

It is an object of the present invention to provide a low cost, PVC-freesealing compound, preferably for use on container closures, whichcontains either low density polyethylene or linear low densitypolyethylene; a styrene-isoprene-styrene block copolymer and/or athermoplastic elastomer mixture of an ethylene-propylene copolymer, suchas EPM or EPDM, EVA and process oil; fillers such as talc, calciumcarbonate, kaolin, titanium dioxide and mixtures thereof; and corkpowder.

It is a further object of the present invention to provide a PVC-freesealing compound with similar or superior sealing characteristics asPVC-based compounds.

It is another object of the present invention to provide a low densitypolyethylene-based sealing compound having a styrene-isoprene-styreneblock copolymer, one or more fillers and optionally cork powder.

An object of the present invention is a PVC-free sealing compound oflinear low density polyethylene, styrene-isoprene-styrene blockcopolymer and one or more fillers.

A further object is to provide a polyethylene-based sealing compound orpolyethylene, such as low density polyethylene or linear low densitypolyethylene; a styrene-isoprene-styrene block copolymer or athermoplastic elastomeric mixture of an ethylene-propylene copolymer andEVA and process oil; and one or more fillers; the sealing compound beinguseful in all applications in which PVC-based sealing compounds areuseful.

It is an advantage of the present invention to provide an inexpensive,PVC-free sealing compound which has all of the desirable sealingcharacteristics of PVC-based compounds, but without the health andenvironmental disadvantages of PVC.

The invention herein is a PVC-free sealing compound of low densitypolyethylene or linear low density polytheylene;styrene-isoprene-styrene block copolymer or a mixture of anethylene-propylene copolymer and EVA and process oil and one or morefillers.

Further objects and advantages of the present invention will be apparentto those skilled in the art from the description and claims below:

DESCRIPTION

The present invention is a PVC-free sealing compound, preferably for useon container closures, comprising:

(a) from about 75 to about 95 parts by weight of low densitypolyethylene (LDPE) or linear low density polyethylene (LLDPE);

(b) from about 10 to about 20 parts by weight of astyrene-isoprene-styrene block copolymer and/or a thermoplasticelastomeric mixture of an ethylene-propylene copolymer, such as EPM orEPDM, ethylene vinyl acetate copolymer (EVA) and process oil;

(c) from about 15 to about 50 parts by weight of one or more fillerssuch as talc, calcium carbonate, kaolin, titanium dioxide and mixturesthereof; and optionally;

(d) from about 0 to about 15 parts by weight of cork powder.

Low density polyethylene (LDPE) and linear low density polyethylene(LLDPE) are known from the prior art, so that no further information hasto be given as to their composition. For reasons of completeness inconnection with LLDPE, it is pointed out that it is not a purepolyethylene, but a copolymer of polyethylene and a small amount ofanother olefin, such as kaprylene (cf. U.S. Pat. No. 4,076,698, whichgives a detailed description of LLDPE, and European Patent ApplicationNo. 9376). A LDPE suitable in the present invention has a melt index of7 and a melting point of approximately 114° C. A suitable LLDPE for thepresent invention normally has a melt index of 3.8 to 5.0 and a densityof around 0.915. An example of a commercially available LDPE is ESCORENELD 251 available from ESSO. A commercially available LLDPE used in thepresent invention is Grade 09-046, from DSM sold by Stamilex.

The styrene-isoprene-styrene block copolymers used according to theinvention are linear polymers (also called segmental polymers), in whichthe ends of polyisoprene chains are in each case terminated bypolystyrene segments (cf. U.S. Pat. No. 4,085,186, particularly column4). Such block copolymers are commercially available with the tradenamesCARIFLEX TR-1107 (Shell), or EUROPRENE SOL T 190 (EniChem). The styrenecontent of the commercially available block copolymers varies fromproduct to product, but is generally between 10 and 40%, so that theisoprene content is from about 60 to about 90%. The aforementionedcommercial products preferably have styrene contents of 15 to 25%. It isimportant that the hardness of these block copolymers is not excessive.Thus, preference is given to those block copolymers with a Shore-Ahardness of 20 to 50 and preferably approximately 30.

The thermoplastic elastomeric mixture which may be used instead of theblock copolymer is a mixture of an ethylene-propylene copolymer, such asEPM or EPDM and EVA and process oil. Reference is made to EuropeanPatent Application No. 00 32 804 with reference to the thermoplasticelastomeric mixture of substantially EPM or EPDM-elastomer, EVA andprocess oil suitable in the present invention. A commercial productsuitable for the purposes of the invention is ESCORENE ULTRA EX 095 (byESSO) with a melt index of 1.5 and a Shore-A hardness of approximately58. These mixtures are also known as elastomeric alloys.

The fillers useful in the present invention are well known to thoseskilled in the art and are commercially available. A preferred filler istalc, having a particle size of 75μ (99% passes through a sieve with a75μ internal mesh diameter). Other fillers include calcium carbonate,kaolin (also known as china clay or clay) and titanium dioxide.Preferably the latter fillers are in a fine powder form, having aparticle size of 50μ (98 or more % pass through a sieve having aninternal mesh diameter of 50μ). Additionally, mixtures of these fillerscan be used in the invention. Other fillers, not specifically mentionedherein, but well known to one skilled in the art, could be used in thepresent invention so long as they do not adversely affect the desiredcharacteristics of the compound.

The amount of filler or fillers used in the present invention rangesfrom about 15 to about 50 parts by weight with a preferred range ofabout 20 to about 40 parts by weight.

An optional, but preferred, ingredient of the present invention is corkpowder. Preferably, the cork powder has a particle size of about 75μ.The cork powder may be added in quantities from about 0 parts by weightto about 15 parts by weight, with the preferred amount being about 10parts by weight.

The sealing compound may be made in any conventional manner. The variousingredients are randomly mixed together to create a blended, homogenouscompound. The compound can be mixed in a standard mixer, such as aBanbury mixer or in any other type of mixer or blender which is normallyused for making sealing compounds.

Preferably, the compound is made by an extrusion/molding technique inwhich the ingredients are fed in the correct proportions to the head ofthe extruder which extrudes the formed compound.

Once the compound has been formed it may be used in any manner similarto those currently in use with PVC-based compounds. For example, drymixture having a powder-like consistency can be used and can beprocessed into webs or sheets under the effect of pressure. These websor sheets are then cut into small plates or disks which can beintroduced into closures as liners. These liners are preferably diepunched into the final shape of the seal. Likewise, the dry mixture maybe introduced directly into the closure and suitably heated andcompressed by a forming die into the desired shape.

Preferably, the compound is extruded into pellets which are then placedinto the closures and formed into seals with a die. Examples of such aprocess are well known in the PVC area, as evidenced by U.S. Pat. Nos.3,696,956 and 3,883,025. These processes are as equally well suited forthe present sealing compound.

Another preferred process is to extrude the compound in a tape form andcut plates or disks out of the tape for use as liners.

The sealing compounds of the present invention are particularly suitablefor use in container closures, preferably bottle closures, such ascrowns, rolled on caps and twist on caps. Such closures can be made fromtin plate, sheet steel or aluminum or plastic.

The following examples are presented to show the various types ofcompounds which can be made under the present invention. These examplesare for illustration only and are not intended in any way to limit thescope of the present invention.

EXAMPLE 1

A compound of the present invention was made of 85 parts by weight oflow density polyethylene having a melt index of 7; 15 parts by weight ofa styrene-isoprene-styrene block copolymer, sold under the tradenameEUROPRENE SOL T 190 by Enichem; and 40 parts by weight of talc having aparticle size of 75μ. The compound was mixed and extruded into pelletform and formed in a closure by a cold die. The sealing characteristicsof the compound equalled those of the presently available PVC-basedcompounds.

EXAMPLE 2

A compound formed similar to that of Example 1, except linear lowdensity polyethylene was used instead. The seals formed by the compoundshowed very good sealing characteristics.

EXAMPLE 3

A compound of 85 parts by weight of low in density polyethylene, 15parts by weight elastomeric alloy, having a Shore A hardness of 58, avinyl acetate content of 10% and sold under the tradename ESCORENE ULTRAEX 095, and 40 parts by weight talc, similar to that of Example 1, wasformed into seals and showed characteristics similar to those of Example1.

EXAMPLE 4

A compound of 85 parts by weight of low density polyethylene; 15 partsby weight of elastomeric alloy, having the same properties as that inExample 3, 40 parts by weight talc; and 10 parts by weight of corkpowder formed seals with sealing characteristics similar to those ofPVC-based compounds.

While this invention has been described with reference to its preferredembodiments, other embodiments can achieve the same result. Variationsand modifications of the present invention will be obvious to thoseskilled in the art and it is intended to cover in the appended claimsall such modifications and equivalents as fall within the true spiritand scope of this invention.

What I claim is:
 1. A sealing compound for use on container closuresconsisting of:a. From about 75 to about 95 parts by weight ofpolyethylene; b. From about 10 to about 20 parts by weight of astyrene-isoprene-styrene block copolymer; and c. From about 15 to about50 parts by weight of a mixture of fillers consisting of talc and corkpowder.
 2. The sealing compound of claim 1 wherein the polyethylene isselected from the group consisting of low density polyethylene andlinear low density polyethylene.
 3. The sealing compound of claim 1wherein the styrene content of the styrene-isoprene-styrene blockcopolymer is from about 10 to about 40%.
 4. The sealing compound ofclaim 1 wherein the amount of polyethylene is 85 parts by weight, theamount of block copolymer is 15 parts by weight, and the amount offiller is from about 20 to about 40 parts by weight.
 5. A sealingcompound for use on container closures consisting of:a. about 85 partsby weight of polyethylene; b. about 15 parts by weight of astyrene-isoprene-styrene block copolymer; and c. from about 20 to about40 parts by weight of of a mixture of cork powder and talc.
 6. A sealingcompound of claim 5 wherein the polyethylene is selected from the groupconsisting of low density polyethylene and linear low densitypolyethylene
 7. A sealing compound consisting of:a. from about 75 toabout 95 parts by weight of polyethylene selected from the groupconsisting of low density polyethylene and linear low densitypolyethylene; b. from about 10 to about 20 parts by weight of astyrene-isoprene-styrene block copolymer wherein the styrene content inthe copolymer is from about 10 to about 40%; and c. from about 15 toabout 50 parts by weight of a mixture of fillers consisting of talc, andcork powder.
 8. A sealing compound of claim 7 wherein the amount ofpolyethylene is 85 parts by weight, the amount of block copolymer is 15parts by weight and the amount of fillers is from about 20 to about 40parts by weight.
 9. A sealing compound of claim 7 wherein the fillersare 40 parts by weight talc and 10 parts by weight cork powder.